\documentclass{standalone}
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\usepackage{amsmath}
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\begin{document}
\small
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  \draw[thin](2,0)--++(0.5,0)node[right]{$+$};
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  \draw[thin](1.3,-0.2)--++(-45:0.7)node[right]{铜圆筒（阴极）};
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\end{document}